Early detection and early treatment of patients suffering from osteoporosis estimated to be a population of ten million and a potential group thereof currently in Japan is important.
Current major osteoporosis diagnostic techniques in Japan are: bone-density measurement of the lumbar spine and the femur by a double X-ray resorption measurement apparatus (DXA) capable of measuring bone density with utmost accuracy; and bone density measurement of the calcaneus through quantitative ultrasonography (QUS) as a simplified method. However, the current state is that only certain facilities are equipped with these apparatus, and are only used for persons with symptoms of osteoporosis such as lower back pain, or persons with great concern for osteoporosis, while not being used for prevention of fractures considered to be caused by osteoporosis.
Recent studies claim that a decrease in bone density may bring about alterations in shape of the cortical bone at the lower edge of a mandible (thick compact bone covering the outer side of the mandible bone) in a panoramic radiograph of all teeth and surrounding bones of the chin (see Non Patent Reference 1). FIG. 1 shows an exemplary panoramic radiograph of teeth. In addition, it is understood that persons with an altered shape of the lower edge of the mandible have a significantly higher risk of fracture due to slight external pressure compared to persons without (see Non Patent Reference 2).
Common dental care does not put diagnosis of osteoporosis using panoramic radiographs into practical use since examination of this mandible inferior border area is infrequent and an examiner's reading ability of X-rays is questioned.
Although studies on diagnosing osteoporosis utilizing panoramic radiographs have mainly been centered on altered shapes of a portion called spongy trabecular bone existing in the maxillary bone and the mandible bone (see Non Patent References 3, 4, 5, and 6), diagnosis by automatically extracting only the trabecular bone from a panoramic radiograph is difficult, and therefore has not been put into practical use. It has also been reported that diagnosis is possible from the thickness of the cortical bone at the lower edge of the mandible (see Non Patent References 3 and 7).
If persons at risk of osteoporosis can be screened using panoramic radiographs, screening of persons without subjective symptoms that are difficult to diagnose or persons without concern for osteoporosis, and instruction for only persons potentially having osteoporosis to undergo closer examination such as DXA or referral to a facility equipped with that apparatus allow early detection and early treatment of patients suffering from osteoporosis, and also reduce costs of the examination. Furthermore, the method used for this screening must be simple and usable even without having any special skills or requiring complicated operations.
However, technology for diagnosing a patient suffering from osteoporosis by, for example, focusing on an altered shape of the cortical bone at the lower edge of the mandible in a panoramic radiograph, and objectively and automatically assessing it through mathematical morphologic image processing using computer software does not exist.    [Non Patent Reference 1] E. Klemetti, et al., “Pantomography in assessment of the osteoporosis risk group”, Scandinavian Journal of Dental Research, 1994, 102, P68-72    [Non Patent Reference 2] A-M. Bollen, et al., “Case-control study of self-reported osteoporotic fractures and mandibular cortical bone”, Oral Surgery Oral Medicine Oral Pathology Oral Radiology and Endodontics, 2000, 90(4), P518-524    [Non Patent Reference 3] J. Negoto, et al., “Study of the relationship between periodontal disease and osteoporosis using parameters of panoramic radiographs and osteoporosis diagnosis”, Japanese Society of Periodontology Journal, 2001, 43(1), P13-24    [Non Patent Reference 4] S. Kumasaka, I. Kashima, Initial investigation of mathematical morphology for the digital extraction of the skeletal characteristics of trabecular bone, Dentomaxillofacial Radiology, 1997, 26, 161-168    [Non Patent Reference 5] S. C. White, et al., “Alterations of trabecular pattern of the jaws in patients with osteoporosis”, Oral Surgery Oral Medicine Oral Pathology Oral Radiology and Endodontics, 1999, 88(5), P628-635    [Non Patent Reference 6] T. E. Southard, et al., IEE Trans. Biomed. Eng.: 43, 123-132(1996)    [Non Patent Reference 7] A. Taguchi, T. Wada, et al., “Osteoporosis the role of dentistry achieving early diagnosis” Hiroshima University Dental Society Journal, 1993, 25, p525-526    [Non Patent Reference 8] T. Tanbe, et al., “Extraction of trabecular bone of the jaw from panoramic radiographs”, The Institute of Electronics, Information and Communication Engineers, 2002, P94